National Geographic : 2016 Feb
Us EXPLORE Light Cornea Retina Shape of normal eye Lens PHOTO: ELLIOTT ERWITT, MAGNUM PHOTOS. NGM ART. SOURCES: IAN MORGAN, AUSTRALIAN NATIONAL UNIVERSITY; MARY FRANCES COTCH, NATIONAL EYE INSTITUTE Us EXPLORE Though some gestures of human affection may be timeless, kissing isn’t one of them. Showing love by passionately locking lips is a fairly recent development in human evolutionary history, says a study by researchers from the Kinsey Insti- tute at Indiana University and the University of Nevada, Las Vegas. It is hardly a universal practice—and some cultures view it as decidedly “gross.” In what its authors say is the first large study of “romantic-sexual” kissing, only 46 percent of 168 cultures surveyed had a social history that included smooching. Middle Eastern and European cultures have embraced such kissing, for example, but sub-Saharan African and Amazonian forager cultures have not. Study author William Jankowiak suggests that kissing may be “linked to the rise of leisure” in socially stratified societies; when the elites took it up, they were mimicked by the masses. “Status trickle-down is ubiquitous in human history,” he says. “And people do seem to like kissing once they discover it.” —Eve Conant A Kiss Isn’t Just a Kiss HARD ON THE EYES Rates of myopia have increased around the world, particularly in Asia. In China about 90 percent of 17- to 19-year-olds are nearsighted, up from an estimated 10 percent in the 1950s. Myopia is pandemic in the U.S. too, reports the National Eye Institute. Once thought to affect bookish children, nearsightedness is now believed to “arise from a lifestyle of not just too much study but of too little time outdoors,” says researcher Ian Morgan. Glasses can clear up vision, but exposure to sunlight seems to be the best defense. A 2013 study in Taiwan found that spending school recess outside can prevent myopia’s onset. —Daniel Stone A myopic eye is more elongated. Light focusing in front of the retina causes blurry vision.